tidy-up: miscellaneous

- curl_ntlm_core, smtp, schannel: fix comments.
- curl_setup.h: fix to undef before define.
- tool_doswin, server/sockfilt: reduce variables scopes.
- tool_doswin: drop an interim variable.
- windows: replace `SOCKET_ERROR` with `0` to align with rest of code.
- libssh2: rename variable to align with rest of code.
- gtls, unit1398: use `#if 0`.
- curl_trc.h, curlx/inet_ntop.h: add missing parentheses in macro
  expressions.
- ldap.c: set empty macro to `do {} while(0)`.
- examples/crawler: rename a non-CURLcode `result` variable.
- CURLINFO_TLS_SESSION: drop stray colon.
- add `const` to casts where missing.
- drop unnecessary parentheses.
- fix indent.
- quote style.
- comment style.
- whitespace, newlines, fold/unfold.

Closes #20554

.github/workflows/linux.yml

@@ -773,7 +773,7 @@ jobs:
           curl --disable --fail --silent --show-error --connect-timeout 15 --max-time 120 --retry 6 --retry-connrefused \
             --compressed https://apt.repos.intel.com/intel-gpg-keys/GPG-PUB-KEY-INTEL-SW-PRODUCTS.PUB | \
             sudo tee /etc/apt/trusted.gpg.d/intel-sw.asc >/dev/null
-          sudo add-apt-repository "deb https://apt.repos.intel.com/oneapi all main"
+          sudo add-apt-repository 'deb https://apt.repos.intel.com/oneapi all main'
           sudo apt-get -o Dpkg::Use-Pty=0 install intel-oneapi-compiler-dpcpp-cpp-and-cpp-classic
           source /opt/intel/oneapi/setvars.sh
           printenv >> "$GITHUB_ENV"